It is known that drilling mud is a heterogeneous liquid system which necessarily contains colloidal solid phase particles. The presence of such particles in drilling mud determines a number of important rheological properties of drilling mud affecting the quality of well drilling. The drilling mud should retain these properties to ensure the best well drilling conditions. However, the stable maintenance of the properties of drilling mud during drilling is a very difficult problem.
The majority of drilling operations are conducted in clayey rocks. Drilled clayey rocks are partially dispersed and admix with the drilling mud in the form of very fine colloidal particles, and this surplus of solid phase should be continuously removed.
Inadequate separation of solid phase from drilling mud after several pumping cycles during well drilling substantially changes the composition of drilling mud, and various methods should be used for improving quality of drilling mud. Therefore, the economical separation of solid phase from drilling mud or, which is the same, the efficient cleaning of drilling mud from drillings is of a paramount importance for the well drilling process.
The technical and economical performance of drilling process depends to a large extent on the quality of the drilling mud used and the degree of its cleaning from drillings.
High-grade cleaning of drilling mud improves the mechanical speed of drilling and conditions for operation of drill bits and equipment. In addition to improving the mechanical speed of drilling, high-grade cleaning of drilling mud contributes to the reduction of consumption of materials used to preserve the adequate properties of drilling mud, prolong the life of the drilling mud and reduce complications and emergency situations during drilling.
A low quality of cleaning of drilling mud is the main reason of emergency situations and complications associated with drilling mud absorption, jamming of drilling and casing pipes, avalanches and fallouts of rock from the well walls.
Therefore, the high-grade cleaning of drilling mud from drillings is the most important production process during well drilling which has a substantial effect on the technical and economical performance of drilling.
All existing methods and apparatus for cleaning drilling mud enable the removal of only a certain portion of the solid phase from flowing (circulating) drilling mud. They all, however, possess a number of disadvantages inherent in the very concept of phase separation on which they are based. Thus, the smallest particle size for separation from drilling mud on vibratory screens depends on the mesh size of the screen. With a reduction of the mesh size to improve the quality of cleaning, the throughput capacity materially decreases and losses of drilling mud with the waste increase.
In cleaning in hydrocyclones, coarse and heavy-weight solid phase particles are removed from drilling mud. Fine and light-weight particles (below 20 .mu.m) appearing upon dispersion of drillings in drilling mud cannot be removed by using hydrocylones and other known cleaning apparatus.
Known in the art is a method for regenerating drilling mud, wherein drilling mud leaving the well and containing drillings is preliminarily diluted and separated from coarse solid phase particles. Fine non-charged drillings and colloidal negatively charged clayey particles are present in the diluted and cleaned drilling mud. Then negatively charged clayey particles are separated from the drilling mud by depositing them on a rotary anode with subsequent removal by means of a scraper. The deposited negatively charged clayey particles entrain therewith a quantity of non-charged particles which are also deposited on the rotary anode. This method only enables the cleaning of a portion of drilling mud, and the remaining portion is fed to the well without cleaning.
The cleaning of only a portion of drilling mud with precleaning to remove coarse particles with subsequent removal of fine particles is complicated and expensive.